AP Bio Unit 7: Natural Selection

molecular evidence

comparing DNA sequences and amino acid sequences in proteins from different organisms

the more recently the organisms share a common ancestor, the more similar their DNA sequences will be

morphology (homologous structures)

homologous structures are structures which have common ancestry but different functions (Ex: human hands, bat wings, whale fins)

vestigial structures

anatomical features that no longer serve a purpose in modern organism but may have had a function in an ancestral organism (ex: tailbone or wisdom teeth in humans)

fossils

existence of fossils from organisms that no longer live on earth show evidence of evolution

convergent evolution

species that live in similar environments may evolve similar adaptations even though they do not share a common ancestor

do individuals evolve?

no; populations evolve

differential reproductive success

individuals with phenotypes that give them a survival advantage are more likelyy to survive + reproduce

directional selection

one end of the range of phenotypes is favored

stabilizing selection

intermediate phenotype is favored; extreme phenotypes are selected against

disruptive selection

individuals on both extremes of the phenotypic range are more likely to survive + reproduce

artificial selection

humans selectively breed domesticated plants/animals to produce populations with desired traits

sexual selection

individuals with certain characteristics are more likely to attract mates than other individuals

intersexual selection

individuals of one sex are particular in selecting mates from the other sex

intrasexual selection

members of one sex compete for mates of the other sex

gene flow

transfer of alleles from one population to another

genetic drift

random loss of alleles in a population (bottleneck + founder effect)

is genetic drift more likely to occur in smaller or bigger populations?

smaller

bottleneck effect

size of a population is greatly reduced for one or more generations

due to natural disasters like hurricanes, fires, floods, volcanic eruptions

surviving population is much LESS likely to possess all the alleles the larger population had before the bottleneck

founder effect

few members of a larger population start a new population (Amish people with Ellis-van Creveld syndrome)

Hardy-Weinberg Assumptions

1. large population size

2. random mating

3. no gene flow

4. no selection

5. no mutations

Hardy Weinberg Equations

p + q = 1

p² + 2pq + q² = 1

the more recent the common ancestor of two species the ——- (closer/farther) their degree of relatedness

Closer

Miller-Urey Experiemnt showed a theory of how life on Earth originated

inorganic materials that were present in Earth’s early atmosphere combined to make the building blocks of biological molecules

Meteorite theory of how life started on Earth

Meteorites transported organic molecules to Earth

Evidence for a common ancestor in all eukaryotes

1. Membrane-bound organelles in all eukaryotes

2. Linear chromosomes in all eukaryotes

3. All eukaryotes have genes that contain introns

species

group of organisms that are capable of interbreeding and producing viable and fertile offspring

speciation

evolution of a new species when two populations are reproductively isolated from each other (prevents interbreeding)

adaptive radiation

divergent evolution of organisms into separate species that occupy different ecological niches

if an environment is relatively stable, there will be _______ (more/less) selective pressure on populations and the rate of species toon will be ______ (faster/slower)

less; slower

gradiualism

slow, constant pace of speciation

punctuated equilibrium

long period of stability interrupted by periods of rapid evolution

allopatric speciation

larger population becomes geographically separated and the smaller subgroups diverge and become separate species over time

sympatric speciation

same geographic area, but other factors lead to reproductive barriers between members of the groups

example of sympatric speciation and what is it

polyploidy - replication of extra sets of chromosomes in plants

sexual selection

prezygotic barriers

prevent formation of a zygote

types of prezygotic barriers

1. Habitat isolation

2. Temporal isolation

3. Behavioral isolation

4. Mechanical isolation

5. Gametic isolation

Habitat isolation

organisms live in different habitats (don’t interact with each other)

Temporal isolation

Organisms live in same habitat, but are active during different times of the day or have different breeding seasons during different parts of the year

Behavioral isolation

Species will interbreed only with others who perform compatible mating behaviors (specific birds songs)

Mechanical isolation

Sexual organs are incompatible, preventing transfer of gametes

Gametic isolation

If their gametes are incompatible, no zygote will be produced

postzygotic barriers

after zygote is formed, these barriers prevent the zygote from developing into a viable and fertile adult organism